Pen



FIG. 1 is a lower front right perspective view of a pen showing my new design;

FIG. 2 is a right side elevation view of the pen shown in FIG. 1, with a left side elevation view being a mirror image thereof;

FIG. 3 is a front elevation view of the pen shown in FIG. 1, with a rear elevation view being a mirror image thereof;

FIG. 4 is a top plan view thereof; and,

FIG. 5 is a bottom plan view thereof. 

The ornamental design for a pen, as shown and described. 